The present invention relates generally to a method and system for pumping fluids and, more particularly, to a submersible pumping system for filling and discharging a fluid reservoir such as the hull of a cargo ship or a land-based storage vessel for liquified gases.
The present invention constitutes an improvement upon the submersible pumping systems disclosed in U.S. Pat. No. 3,369,715 to James C. Carter, and U.S. Pat. No. 3,876,120 to William G. Haesloop. In such systems a pump and motor unit is lowered into a vertical casing extending through a storage reservoir for liquified gases. The unit trips a normally closed foot valve at the bottom of the casing to communicate the pump inlet with the liquid in the reservoir. The centrifugal pump of the unit pumps the liquid into the casing where it flows upwardly to an outlet port at the top of the casing. When the unit is raised off the foot valve, the foot valve closes sealing the casing from the reservoir so that the unit may be removed for repair or replacement.
In the aforementioned systems, there may be a small degree of leakage of liquid or gas from the reservoir through the foot valve to the casing interior when the foot valve is closed. In some applications, it is essential or desirable that no such leakage exist or that such leakage be reduced to an absolute practical minimum. It is the purpose of the present invention to provide an extremely low leakage foot valve which will prevent the loss of any liquid or liquified gas in the casing and prevent any possible hazards of venting flamable gases to the local atmosphere when the casing top has been opened.